When James Vincent McMorrow performs, he squashes himself up behind a keyboard, feet apart and knees together, looking a little like a collapsed laundry rack. The 30-year-old's right hand shakes from the beginning of a song to its end. You give up drink, as the Dubliner did two years ago, and "all of a sudden the nerves come back.

"I was never nervous before: there's an instrument, pick it up, play it; if I make a mistake, who cares? I wasn't always aware of the importance of this job. I'm aware of it now, I appreciate it, I'm here, I've got one opportunity… I sound like fucking Eminem. But it's true. You get one chance to make an impression and coasting through is a disservice."

McMorrow releases his second album, Post Tropical, on 13 January. Forgive the hasty praise, a week before the reviews are due and the out-of-10s confirmed, but I think it's stunning: plump synths under McMorrow's gliding, grainy vocal; the lyrics tight and worked-at. His first album, 2011's Early in the Morning,was tagged by many as folk, or nu-folk – "because I have a beard," McMorrow guesses. Perhaps to confound all this, the tracks on his follow-up are denser, no acoustic guitars audible, everything brazenly laptop-meddled. There's a flavour of James Blake and second-album Bon Iver.

"I have no interest in making music that's built for an antique shop," says McMorrow. "I love that it's 2013, 2014 – I love that I can do these things with technology. It bothers me when musicians listen to music from the 60s and try and recreate it. Those people weren't trying to recreate music from the 20s. Why do it?"

Before we met, I watched him perform some tracks from the new album for Lauren Laverne's 6 Music radio show. It was a short set, tucked in after the midday news; when it was time for McMorrow to sing, an item about George Osborne's autumn statement had just ended. We were in an ugly little room on the fourth floor of the BBC's central London studio, boxes of printer toner piled around. The Chancellor's awful voice had been yapping out over the airwaves, and for a few minutes McMorrow overrode it all with real beauty.

"I wanted to make something that was beautiful in whatever it did, wherever it went," he says of Post Tropical. McMorrow frequently interrupts his paragraph-length declamations to apologise for cheesiness, or anything that sounds sound-bitey, but he doesn't mind admitting he finds his new album pretty good. "In interviews like this I used to round out the edges of what I thought. I'd say, 'Do you like that? OK, I like that too.' That's not true to the person I am."

So instead? "Just be real, don't bullshit people. It's like half the campaign of selling a record is trying to convince people that you're an artist. Well, I am an artist. This is what I do. I don't have to get Jeff Koons to make a fucking replica of me to try and convince you that it's art."

I presume this is a reference to Lady Gaga, whose last album, Artpop, had a cover by Koons. McMorrow says it in a London pub, around the corner from the BBC studio. In grey jumper and jeans, his beard rather wild and the hair starting to thin on top, he stirs his tea with a finger. "If you believe in it, it's art. You don't have to convince people. And if you do, maybe you're going about it wrong."

London has mixed associations for the Irishman. It was here, after a tour-ending show at the Royal Festival Hall, that he decided to give up booze. (Amnesia was a clincher: "The biggest show I'd ever played in this country… I got off stage and thought: did that go well? I didn't know.") And back when he was starting out, a young singer-songwriter thought to be full of commercial promise, London was the scene of crushing disappointment.

McMorrow signed a deal with EMI/Universal at 24, told: come to London! Glad-hand! "So you're taken into Universal's 'Death Star' building [in west London] and everything is fantastic. You play a couple of shows, and these label guys come – and they leave halfway through a show. Then the phone calls just stop. And your heart is broken. At that point, I just didn't have it figured out. I wasn't committing. I wasn't in love with the songs I was playing to these people, so of course they weren't going to give a shit about it."

Having been flattered, taken out for dinners, "smoke blown up [his] arse", McMorrow was abruptly cast out of Universal's Death Star. He flew back to Dublin from London feeling "dejected". He didn't have the useful infrastructure of big-corp music around him, but then "I was free to do whatever I pleased. It certainly wasn't my ideal situation, but I knew that I had to [make some music] that I connected with. So it was six months of really unspectacular graft, chipping away at songs."

McMorrow recorded Early in the Morning in Drogheda, on Ireland's east coast, more or less on his own, in a little studio by the sea. Which looked great on the press release, even if it was a case of contingency rather than exotic, monkish withdrawal. "I didn't have any options. No money."

Once the record was out, it took time to find an audience ("Nobody gave a shit for a year"), but one of the tracks was picked up for use on Grey's Anatomy and the LP started selling in Ireland, later in the UK. That Royal Festival Hall gig, unremembered by McMorrow, was a sell-out in February 2012.

He decided to work on his second album "the only way I knew" – in seclusion, this time removing himself to a remote studio in Texas. "I like my own musical company – to the point where, if other musicians are in the room, I actually seize up a bit, tend to not believe in my own ideas."

McMorrow gives as an example the second song on Post Tropical, The Lakes. "I wanted it to start by sounding like a waterfall. And if I said that in a room… they'd say it doesn't mean anything. But not having other musicians with me meant that I got to live with the idea for a little minute."

He worked it over, trying picking patterns on a guitar, adding delays and distortions. "I brought Emma, my girlfriend, in to listen to it. I didn't say anything. She had her eyes closed, and this sounds incredibly cheesy but, genuinely, the first thing she told me was, 'It sounds like a waterfall.' I thought, OK! I thought, this is not a crazy instinct! I thought…"

Marry this girl?

"Absolutely."

McMorrow and his girlfriend manage to pull off the trick of collaborating professionally while remaining a happy couple. A photographer and illustrator, Emma Doyle took the picture he used on the cover of his first album, and she painted the cover for his second, a riff on an old Hawaiian postcard they have tacked up at home. "It's a gift to be able to do this job," McMorrow says, "and it's a gift to be able to share it with someone you love."

They met through mutual friends when McMorrow was doing a show in Galway, where Doyle was at university. This was around the time that London was licking its lips at him. A&R men were flying in for gigs and McMorrow was full of beans. But he almost messed it up with the girl. "We were hanging out that evening… I have a beautiful old guitar and Emma dropped it. I thought, 'God damn!' I was so mad. I grabbed it, threw everyone out, went to sleep. And I didn't see her again for months."

They worked it out, despite the temper tantrum. McMorrow is aware that he can come across as spiky: "I like what I like, I don't like what I don't like, and I'm very bad at toning myself down." He regrets, now, an early reputation he had for belligerence at gigs. Rambling, half-arsing chords, saying to a noisy audience member once: "Fuck you, I have your money."

But all that was when he and his band were routinely seeing off multiple bottles of red before gigs, passing more about on stage – once even at a dry gig at a London church where the audience could be assumed to be sober and probably unimpressed.

"When you're touring, it's the greatest party in the world. Until it turns into the worst party in the world – quickly. This job is about more than drinking on stage and talking shit into a microphone. You can give a 70% performance and people would probably still dig it. But I don't want to do that any more. I want there to be that agitation, that shake in my hand, every time. Because that means that I care enough to shake."